Which numbers are irrational? Select the three that apply.

To determine which numbers are irrational, let's first identify the values of each option:

1. **√9** = 3 (which is rational)
2. **√169** = 13 (which is rational)
3. **Pi (π)** is approximately 3.14159 and is known to be an irrational number.
4. **√18** = 4.24264... (which is irrational, as it cannot be simplified to a fraction)
5. **√78** = 8.83176... (which is also irrational)
6. **9/15** = 3/5 (which simplifies to a rational number)

The three numbers that are irrational in the provided list are:
- Pi
- √18
- √78